Lab Science News

The Department of Antiquities Conservation of the J. Paul Getty Museum recently requested assistance from CAS’ Simi Valley Air Quality Laboratory to sample and analyze the atmosphere surrounding a second century Egyptian mummy. About six years ago, the mummy was sealed in a case containing ambient air. The museum wished to determine the volatile and semivolatile organic compounds off-gassing from the mummy. One purpose of the study was to determine the impact of off-gassing on other artifacts that were to be displayed with it.

Compounds of interest included low molecular weight organic acids, volatile organic chemicals, and the semivolatile compound, guaiacol. Guaiacol is a component of cedar oil and one of the embalming fluids used by the Egyptians.The other chemicals were associated with previous restoration activities with the mummy.

In order to collect the samples, two holes were drilled in the case housing the mummy. Sampling ports consisting of Teflon tubing (1/4” OD) and a ferrule and female Swagelok fitting were installed in the holes. The ports were sealed off at the time of installation and only opened during sampling periods.

Two sampling and analytical methods were used to address the compounds of interest. Volatile organic compounds were sampled in evacuated passivated stainless steel canisters (SUMMA-like) and then analyzed for tentatively identified compounds (TICs) by gas chromatography/ mass spectrometry (GC/MS) following US EPA Method TO-15. This technique involves identifying the most predominant compounds by Jeanette Campbell - Simi Valley, CA in the sample by comparing their mass spectra with those from the NIST library, which contains mass spectra from more than 120,000 compounds. Heavier compounds were sampled on Tenax TA tubes and then thermally desorbed and analyzed by GC/MS following EPA Method TO-17. These samples were analyzed for guaiacol and other TICs, including acetic acid.

Compounds of both biogenic (e.g., isobutyric acid) and synthetic origin were identified in the samples (see Figure 1 on page 3). Acetaldehyde, 3-methylbutanal, pentanal, furfural and methyl methacrylate were present above their odor threshholds. Several of these compounds had an “odor character,” that might have contributed to the “characteristic mummy odor” described by one of Getty’s researchers.

An important outcome of this project was the side-by-side comparison of the efficacy of two sampling methodologies that are frequently used to evaluate organic compounds in indoor air investigations. Neither media type collected the full range of compounds of interest. Lighter compounds were only detected in the SUMMA-like canister sample. In contrast, heavier, higher boiling point compounds were only identified in the samples collected on the Tenax sorbent tube. Midrange compounds (e.g., boiling points of 70oC to 240oC) were detected using both sampling media and showed similar quantitative and qualitative results.

Although boiling point appeared to be the primary determinant of the compounds that were collected by the two types of media, other properties (vapor pressure, polarity, lability) may also have had an impact. For example, the labile compound, isobutyric acid, was only detected in the solid sorbent samples even though its boiling point (155o C) is in the more volatile range, which may be collected by SUMMA canisters.

The Mummy project presented the laboratory with a unique opportunity to evaluate an environment containing a wide range of compounds. The results of this project suggest that for indoor air investigations, the use of multiple sampling media may generate more meaningful data than reliance on a single type.

CAS would like to thank Cecily Grzywacz, Scientist in the Science Department of the Getty Conservation Institute and Marie Svoboda, Associate Conservator of Antiquities at the J. Paul Getty Museum for allowing us to present the results of their project.

Diffusive sampling has been a popular approach for the evaluation of workplace exposures to airborne contaminants, such as volatile organic compounds (VOCs) for some time. Typically, these “badge-type” samplers (e.g., 3M, SKC) have been used to evaluate exposures in the high part per billion (ppb) to part per million (ppm) range over an 8-hour period. A popular option, these samplers are easy to use, small in size and don’t require a sampling pump.

This approach involves the passive collection of an analyte on a solid sorbent via adsorption or chemical reaction. The sampling rate (e.g., diffusive uptake rate) is a function of the diffusive coefficient, which is compound and sorbent specific, and the geometry of the sampler used. Other factors that affect performance include temperature, pressure, humidity, air velocity and transient changes in contaminant concentrations. Samples are chemically desorbed and analyzed by gas chromatography with flame ionization detection (GC/FID) or by other appropriate instrumentation.

More recently, investigators have begun utilizing these devices for applications involving lower levels of contaminants over longer periods of time. This usage has become feasible with the development of passive samplers containing solid sorbents that may be thermally rather than chemically desorbed . This application of diffusive sampling can be useful for risk assessors and others wishing to evaluate airborne contaminant levels over extended periods of time (e.g., weeks to months).

Previously, the absence of an established method and the fact that very little data are available for longer term applications (e.g., greater than 8 hours) has proved limiting. Earlier this year, the International Organization for Standards (ISO) published a document , which defines a sampling and analytical method and also includes sampling rates for a wide range of compounds on numerous types of sorbents.

CAS Simi Valley is currently involved in a project being conducted by a regional air pollution control agency that is looking at the feasibility of utilizing diffusive samplers to monitor sub ppb levels of benzene, methylene chloride, trichloroethene and tetrachloroethene over a 30 day period. This project has presented some unique challenges that highlight some of the parameters to consider before selecting this methodology. The goal was to select a single sorbent for which there were documented sampling rates for each of the compounds of interest (preferably based on long term studies), that was also strong sorbent and hydrophobic. Chromosorb 106 was selected because it was the best compromise based on the available data.

The use of passive diffusive samplers coupled with analysis by thermal desorption/GC/MS may be a valuable tool for situations where individuals wish to monitor low level exposures over a long duration.